Principles Of Chemistry Flashcards
Why do ionic compounds not have molecular formula?
Ionic compounds do not have molecular formula
Cos they DO NOT EXIST AS MOLECULES
The Periodic Table is arranged in order of
increasing atomic no.
All elements in the same period have…
All elements in the same period have the same no. of ORBITAL SHELLS
(He is period 1!!)
Groups in vertical columns have..
Groups in vertical columns have
>same no. Of electrons in outer shell
>similar properties+reactions
How many electrons does He have in its outer shell?
2e- unlike rest which have 8e-
In the noble gases , does density increase up or down the group?
In the noble gases density INCREASES
DOWN THE GROUP
When a compound is heated and broken down into its elements— what name is given to this type of reaction.
Thermal decomposition
Give the definition of ELECTROLYSIS
Electrolysis is a chemical change caused by passing electric current thru an ionic compound ( which is either molten or in solution)to set free the elements
What must there be in order for something to conduct electricity ?
Charged particles.
Either e- or ions
Describe structure of metals
A lattice structure of +ve ions surrounded by a sea of delocalised e-
Why do ionic compounds only conduct electricity when molten or in solution?
Because when ionic compounds are solid the ions are not free to move around, but when molten the IONS r free to move around
What are ANIONS
-VE ions
What are CATIONS
+VE ions
Why do covalent compounds not conduct electricity?
Because they have NO CHARGED PARTICLES (all e- r held tightly in the atoms or in the bond)
What covalent compounds conduct when dissolved in water and why?
HCl gas + AMMONIA gas get ionised in water — therefore their e- are free to move around and conduct
Define the term electrolyte
Electrolyte is a liquid or solution that undergoes electrolysis. Either molten/aq compounds OR solutions containing ions
What are electrodes usually made of and why
Either graphite or platinum cos they’re CHEMICALLY INERT.
What’s an ANODE
+VE electrode
What’s a CATHODE
-VE electrode
What r molten compounds also called
A melt
What electrode does reduction always occur at?
Reduction always occurs at the CATHODE (-VE electrode)
What electrode does oxidation always occur at?
Oxidation always occurs at the anode(+VE electrode)
Give the definition of IONIC BONDING
It’s the transfer of electrons from a metallic atom to a non- metallic atom
In doing so a +ve metal ion and -ve non metal ion is formed — the strong electrostatic attraction between the oppositely charged ions is an Ionic bond
Name the force that holds the ions together in an ionic compound
Strong electrostatic attraction
Why can’t nitrate ions form ionic compounds with bromide ions
Because both nitrate ions and bromide ions are negatively charged
Ionic compounds can only be formed between positive + negative ions
What is the charge of a hydrogen ion
H+
What is the charge of a hydroxide ion
OH-
What is the charge of a ammonium ion
NH4^+
What is the charge of a carbonate ion
Co3^ 2-
What is the charge of a nitrate ion
NO3^-
What is the charge of a sulfate ion
SO4^2-
Why do compounds with giant ionic structures have high melting + boiling points
The electrostatic attraction between the oppositely charged ions is very strong and therefore a lot of energy is needed to overcome them … hence a high melting/boiling point
What should one use to filter a solution
Filter paper
What is an intermolecular force?
Force of attraction between covalent molecules — much weaker than the covalent bonds in a molecule
Explain how the covalent bonds in the water molecule hold the hydrogen + oxygen atoms together
Strong electrostatic attraction between shared 2 electrons and nuclei (of hydrogen and oxygen)
Why do covalent compounds not conduct electricity
Because they have no free electron + no ions
What covalent compound conducts electricity and why
Graphite because it has delocalised electrons, as each carbon atom has only 3 bonds leaving 1 electron free
Why do simple molecular structures with a high relative molecular mass have higher boiling points?
Because the intermolecular forces between molecules with a high relative molecular mass are STRONGER.
As there are more points along larger molecules for the intermolecular forces to act between— so more energy is needed to break the forces(hence higher boiling point)
Why is C60 FULLERENE a poor conductor of electricity
Because although each carbon has one delocalised e-, the electron can’t move between molecules so it’s a poor conductor
Why does diamond not conduct electricity
Because it has NO free electrons or ions
Why does C60 Fullerene have a lower boiling point than diamond ?
Because it does not take as much energy to break the intermolecular forces of attraction in C60 FULLERENE compared to breaking the strong covalent bonds in diamond
What forces is the simple molecular stucture C60 fullerene held together by
Intermolecular forces are the only forces that hold c60 Fullerene together
The layers can slide over each other, that’s why it’s a soft solid
Explain why graphite conducts electricity
Because each carbon atom in graphite has only 3 covalent bonds, so 1 e- is left delocalised and free to move— conducting electricity
Explain why graphite has a high melting point
Because it’s a giant covalent structure and the strong covalent bonds r hard to break
Why do simple molecular structures have low melting boiling point/ (I.e. exist as liquids/gases or solids with low meliting points)
Because they have weak intermolecular forces, and not a lot of energy is required to break them
What is an allotrope
Different forms of the same element
Why is graphite soft and slippery
Although the covalent bonds are v strong, the attractions (aka INTERMOLECULAR FOCES) between the layers are much weaker and not a lot of energy is required to overcome them
Diamond, graphite + C60 Fullerene are 3 ______ of carbon
Diamond, graphite + C60 Fullerene are 3 allotropes of carbon
Is a high or low temperature required to turn carbon to diamond if it’s enthalpy value is +37
A high temperature cos the energy required to break the covalent bond is +ve value meaning it’s an endothermic reaction which absorbs heat
The bonding in a hydrogen molecule is strong.
Explain why the boiling point of hydrogen is low
Because although the bonding in each hydrogen molecule is strong
The intermolecular forces between individual molecules is weak and therefore little energy is required to overcome them
Explain how to atoms in a chlorine molecule are held together
The 2 atoms share electrons which hold them together in a covalent bond, which is the electrostatic attraction between the shared pair of electrons and the nuclei of both atoms
What is an element
Substances that can’t be split into anything simpler by chemical means. CONTAIN ONLY 1 TYPE OF ATOM
What is a compound
When 2 or more different elements chemically combine
Why is sulfur yellow in colour and iron sulfide not?
Cos iron sulfide is a compound and sulfur is an element
The properties of a compound are often completely different to the properties of the original elements
(so a compound of sulfur is not yellow like the element itself)
Why are compounds hard to separate and mixtures not?
Because in compounds the atoms are chemically bonded together whereas in a mixture there is no chemical bond
So a mixture can just be separated by physical methods such as distillation
What is a mixture
When various substances are mixed together w NO CHEMICAL BOND between them
Pure substances have a ___ boiling point whereas mixtures….
Pure substances have a FIXED boiling point whereas a mixture MAY MELT/ BOIL OVER A RANGE OF TEMPERATURES
What is the liquid that has gone thru the filter paper called
FILTRATE
What is crystallisation used for?
Crystallisation is used to separate a solute from a solution
Separate a soluble salt from a solution
CRYSTALLISATION METHOD
1) pour solution into evaporating basin
2) heat + once H2O has evaporated (u will see crystals start to form as it becomes insoluble) remove dish cos this is the POINT OF CRYSTALLISATION
3) filter the crystals out of the solution + leave to dry (use a DESSICATOR)
What is a dessicator
It dries things out by removing water from surroundings using chemicals
Why is simple distillation more often used than crystallisation at separating a mixture
Because in crystallisation the water is lost = a waste
Simple distillation saves the water
Why do substances in a mixture separate on a chromatogram ?
Because the substances in a mixture have different attractions to the paper or solvent
What word is used in chromatography when the ink doesn’t travel far up the chromatogram
STATIONARY PHASE
cos the ink doesn’t travel far with the solvent + is attracted to the paper
What word is used in chromatography when the ink travels far up the chromatogram
MOBILE PHASE
Cos the ink is attracted to the solvent + moves a long way w it
Design an experiment to investigate the composition of a dye with paper chromatography
1) put different spots of ink using a teat pipette in a line on filter paper
2) draw pencil line below for solvent to go into ( don’t touch ink w/ solvent as it will dissolve in)
3) fill up to the line w solvent (e.g. water)
4) place a lid to stop solvent evaporating
5) the solvent will carry the dyes w it , wait till dry— now mark a line where the solvent goes up to
Why might the dots of dye on a chromatogram not move from the pencil line during an experiment… how do we fix it?
The dye may be insoluble + therefore u need a different solvent
How does one work out the Rf values on a chromatogram ?
Rf = distance travelled by sample
——————————————
distance travelled by solvent
(Always measure distance by sample from the MIDDLE of the dot)
How does one find a mole of an element? and what is a mole?
1 mole of a substance =
RAM/ RFM in GRAMS
A mole is the amount of a substance
If the mass number of Sulfur is 32 what is the mass of 1 mole of sulfur
1 mole of sulfur = 32 g of sulfur
How many atoms are there in a mole
6.023 x 10^23 atoms = 1 mole
Number of moles =
Number of moles = mass
————
RAM
Why is % yield not 100%? (Give 3 reasons)
- not all reactants used up
- products escape the reaction vessel
- REVERSIBLE reaction
What is 1 dm^3 in cm^3
1dm^3 = 1000cm^3
Explain the difference between a strong acid and a weak acid
A strong acid is completely ionised in solution (has a pH of 1-3)
whereas Weak acids are not completely ionised (has a pH of 4-6)
